php - using SimpleXML to parse OAI PMH file

I'm trying to parse this file: http://mdc.cbuc.cat/cgi-bin/oai.exe?verb=ListRecords&metadataPrefix=oai_dc&set=afcecemc&from=2011-06-21&until=2011-06-21 using SimpleXML.

I can get all elements but those wich are inside the tag. It says that the tag is empty. Here is my code.

function getXMLfile($URL) {
    $chDyn = curl_init();
    curl_setopt ($chDyn, CURLOPT_URL, $URL);
    curl_setopt($chDyn, CURLOPT_RETURNTRANSFER, 1);
    $xml = curl_exec($chDyn);
    curl_close($chDyn);

    try {
        $xmlObj = new SimpleXMLElement($xml);
    }
    catch (Exception $e) { echo $e; }

    return $xmlObj;
}


$cdmURL = "http://mdc.cbuc.cat/cgi-bin/oai.exe?verb=ListRecords&metadataPrefix=oai_dc&set=afcecemc";

$xmlObj = getXMLfile($cdmURL);
$xmlNode = $xmlObj->ListRecords;

foreach ($xmlNode->record as $rNode) {
    var_dump($rNode->children());
}

But the output is this one:

[...]
["metadata"]=>
  object(SimpleXMLElement)#8 (0) {
}

This element is not empty! I know that the solution is somehow related with using "namespaces" but I can't figure out how to make it works.

Any help it will be appreciated! Thanks.

Solution

To access children with their own namespace, you have to tell SimpleXMLElement that you want children not in the default langauge. See SimpleXMLElement::children.

The document you linked makes use of multiple namespaces so it's probably a bit confusing if you're new to it.

The following is some example code which extends yours (and simplifies the loading a bit but I think you understand it) to access the children inside the first record element (I break the loop):

$url = 'http://mdc.cbuc.cat/cgi-bin/oai.exe?verb=ListRecords&metadataPrefix=oai_dc&set=afcecemc&from=2011-06-21&until=2011-06-21';

$xmlObj = simplexml_load_file($url);

$xmlNode = $xmlObj->ListRecords;

foreach ($xmlNode->record as $rNode) {
    var_dump($rNode->children());
    var_dump($rNode->metadata->children('oai_dc', 1));
    var_dump($rNode->metadata->children('oai_dc', 1)->dc->children('dc', 1));
    break;
}

This gives the following output which I guess is what you're looking for:

object(SimpleXMLElement)#7 (2) {
  ["header"]=>
  object(SimpleXMLElement)#9 (3) {
    ["identifier"]=>
    string(29) "oai:mdc.cbuc.cat:afcecemc/521"
    ["datestamp"]=>
    string(10) "2011-06-21"
    ["setSpec"]=>
    string(8) "afcecemc"
  }
  ["metadata"]=>
  object(SimpleXMLElement)#10 (0) {
  }
}
object(SimpleXMLElement)#10 (1) {
  ["dc"]=>
  object(SimpleXMLElement)#8 (0) {
  }
}
object(SimpleXMLElement)#7 (12) {
  ["title"]=>
  string(12) "Puig d'Assas"
  ["creator"]=>
  string(26) "Gallardo i Garriga, Antoni"
  ["date"]=>
  string(19) "[Entre 1912 i 1928]"
  ["relation"]=>
  array(2) {
    [0]=>
    string(72) "Paper; gelatina i plata; positiu; blanc i negre; horitzontal; 12 x 17 cm"
    [1]=>
    string(27) "Estudi de la Masia Catalana"
  }
  ["subject"]=>
  string(9) "Muntanyes"
  ["coverage"]=>
  string(32) "Puig d'Assas ; Osona ; Catalunya"
  ["description"]=>
  array(2) {
    [0]=>
    string(2) "Bo"
    [1]=>
    string(163) "Títol atorgat pel catalogador. Informació extreta dels àlbums de l'EMC: Situació: Puig d'Assas. Facilitada per: Antoni Gallardo i Garriga. Facilitada en: 1928."
  }
  ["publisher"]=>
  string(33) "Centre Excursionista de Catalunya"
  ["source"]=>
  string(29) "Memòria Digital de Catalunya"
  ["type"]=>
  string(5) "Image"
  ["rights"]=>
  string(49) "http://creativecommons.org/licenses/by-nc-nd/3.0/"
  ["identifier"]=>
  string(35) "http://mdc.cbuc.cat/u?/afcecemc,521"
}